1. Field of the Invention
The present invention relates to a device and process for forming a matrix cavity in an embossing device for paper processing machines.
2. The Prior Art
It is a common practice to emboss letter envelopes, paper napkins, paper handkerchiefs etc., with a design such as a company logo. Such embossings are produced in a paper processing machine in the course of the manufacturing process. Almost finished letter envelopes, letter envelope blanks, paper napkins, paper handkerchiefs etc. are embossed between two cooperating embossing dies, i.e., a top or counter die and a bottom die or matrix.
It is known to the manufacture both the top and counter die or the matrix from hardened steel, which offers the advantage of high resistance to wear. However, the manufacture of the top and bottom dies is very costly. Furthermore, the dies must be aligned with absolute precision because misalignment causes damage to the workpiece to be embossed and to the die itself.
Furthermore, it is known to manufacture the raised embossing die, i.e. the top die from hardened steel, and to employ a softened copper plate as the counter die. With this combination, the raised embossing or top die is pressed into the copper plate in the course of the run-in process, and a negative copy of the top die is produced in the plate, and forms a matrix cavity. It is advantageous in this process that the top die and the matrix so produced within the production machine are in precisely aligned positions relative to each other, and that their fitted form relative to each other is correct. However, this process has the drawback of a long run-in period in the production of the matrix cavity, and a large stress on the roll bearings.
Embossing dies have become known more recently where a top die produced from hardened steel is operating against a matrix made from a material with tough elasticity, e.g. plastic. This leads to excellent embossing results if the paper is not too thick. With this material combination, too, the cavity of the matrix is formed in a plate made from tough elastic material in the course of the run-in phase by the hard top die. This process is very time consuming and, on the average, lasts between 4 and 5 hours. Therefore, the running-in process is not carried out in a production machine itself.